Safety device for microwave ovens



June 8, 1965 G. A. R. OJELID 3,188,441

SAFETY DEVICE FOR MICRWAVE OVENS 4 mea uarcn 1. 1961 sheets-sheet 1 .Fame 1955 ca. A. R. JELxD 3,188,441

SAFETY DEVICE FOR MICROWAVE VENS Filed March l. 1963 2 Sheets-Sheet 2 United States Patent O 3,188,441 SAFETY DEVICE FOR MICROWAVE OVENS Gran Axel Runo jelid, Huskvarna, Sweden, assigner to The present invention relates to a safety device for microwave ovens or furnaces.

In ovens for preparing food by means of dielectric heating provided by short electromagnetic waves (of the order of cm.) fed into the oven space from a generator there has been used, in the prior art as protection against radiation when the food is taken out from the oven, only such switches or circuit breakers as accomplish disconnection of the generator by breaking the operating current of a relay. The disconnection according to that prior method is, however, not entirely reliable, as the relay, due to thermal as well as magnetic reasons, may remain in operative position even after its operating current has been interrupted.

The principal object of the present invention is to provide a safety device which ensures disconnection of the generator' independent of the return movement of any released means and prevents access to the oven space until disconnection has been accomplished.

With these and other objects in view the safety device according to the invention comprises a switch provided in the main supply circuit of the generator of the oven and having a stationary contact means and a movable contact means which is connected with the door of the oven by means of an inelastic device for separating said stationary and movable contact means from each other in response to an initial opening movement of the door and for releasing the door for continued opening movement only in dependence on the displacement of the movable contact means.

Further objects and advantages of the invention will become more fully apparent from the following description and the accompanying drawings illustrating some preferred embodiments of the invention, and in which:

FIGURE l is a diagrammatic side view of an oven provided with a door, a coupling device and a switch;

FIGURE 2 is a longitudinal section of a preferred coupling device; and

FIGURE 3 is a side view, partly in section, of a modified coupling device.

Referring to FIGURE 1, an oven space 1 is connected to a high frequency generator 2 and is provided with a door 3 pivoted on trunnions 23. The generator 2 is connected to theelectric supply network through a transducer or transforming device 4 and a switch 5. Between door 3 and switch 5 there is provided a mechanical connection in the shape of a bar 7 and a coupling S. The switch is encased, triple-pole, and is provided with a strong spring 6 urging the movable contact means 1t) of the switch away from the stationary contacts 11 thereof. Said contact means may be brought in contact with one another through the pressing in of a rod 12. Between rod 12 and bar 7 there is provided `a coupling 8. It comprises a sleeve 15 rigidly fastened to rod 12 and freely movable in an outer sleeve 16 which is rigidly secured to the casing 9 of the switch 5, and a plurality of steel balls 17, preferably three in number. Balls 17 are movable, to a certain eXtent,'in radial openings 18 in the sleeve 15. The radial motion inwards of the balls 17 is restricted due to the conical shape of the openings 18, and the radial motion outwards of the balls is restricted by the outer sleeve 16. This sleeve, however, has two different inside diameters, as shown at 19 and 20 respectively. Sleeves 15 and 3,188,441 Patented June 8, 1965 16 also concentrically surround an end portion of the bar 7 when it abuts the rod 12, and the balls then are located opposite a circumferential groove 21 in rod 7, as shown by solid lines in FIGURE 2.

The device operates as follows:

When the door 3 is shut, bar 7, which is coupled to the door 3, by means of a link 22, maintains the rod 12 pressed in, and switch S-is thereby maintained closed. Current may thus be applied to the unit 4 from the main supply network and drive the generator 2. If the door 3 should now be opened, the spring 6 normally causes the rod 12 to follow the forward motion of the bar '7 (leftwards in FIGURE 2) and thereby separate the movable contact means 10 from the stationary contact means 11, so that generator 2 immediately ceases to operate. If spring 6 for some reason should not be able to displace the rod 12, e.g. if contact means 10 should have been welded to contact means 11 on account of an eX- cessivecurrent passing therethrough, coupling 8 will go into action.

Balls 17 are held in engagement with the circumferential groove 21 of the rod 7 by the sleeve 16 and thereby form a rigid pull connection between door 3 and movable contact means 10. Only when contacts 10 and 11 have been separated and sleeve 15, on account thereof, has been displaced to such an extent that balls 17 have become located in the larger inside diameter of the sleeve 16, do the balls slide out of the groove 21 and release bar 7. If the contacts 10 and 11 should have been so firmly welded together, that 4they cannot be separated through the action of door 3, then the door 3 cannot be opened either.

This embodiment may also be modified, within the scope and spirit of the invention, for instance, in that pawls rockably pivoted in the sleeve 15, and adapted to engage recesses in the bar 7 under the control of the v sleeve 16 may be substituted for the steel balls 17.

In the embodiment of the invention illustrated in FIG- URE 3 the safety device comprises a longish slide 25 slidable in its longitudinal direction and connected, by means of a link 22, with the door 3 at a point above its trunnions or pivot axis 23. Slide 25 is provided with a transverse groove 26 of V-shaped cross section acting as a cam. This cam or groove 26 is adapted to actuate a leaf spring 27 resting in the groove, so that the spring in its turn displaces an operating rod 28 comprised of a bi-polar switch 5a when the door of the oven is opened. The movable contact means 10a are biased in closing direction by means of compression spring 6a, and the oper, ating rod 28 is provided with collars 29. These collars, against which the movable contact means lila bear, displace the movable Contact means without any aid of a spring, and interrupt the electric connection when the rod 2S is pressed upwards by the leaf spring 27. As in the embodiment illustrated in FIGURES 1 and 2 the switch 5a is provided in the electric connection of the generator with the electric supply network and therefore interrupts this connection when the door 3 is opened. The interruption is positive, since no resilient means are included in the connection between the door 3 of the oven and the movable means 10a of the switch 5a.

While the invention has been particularly shown and described with reference to some preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What I claim is:

1. In a micro-'wave oven: an oven space; a pivotal door through which access may be had to said oven space; a high frequency generator coupled to said oven space for supplying high frequency energy thereto; circuit means connecting said high frequency generator with ter- Basen/i1 means between said terminals and said voltage converting and increasing means and having at least one pair of stationary contacts and at least one pair of movable contacts, said movable contacts being conductively interconnected and adapted to bridge said stationary contacts in the operative position of said movable contacts, and a mechanical connection, positively connecting said doorrwith the movable contacts ofsaid switch during the initial opening movement of said door and comprising a rod-like member, said rod-like member being linked to said door 'adjacent to the pivot axis of said door V,and movable approximately in its longitudinal direction in response to opening movements of said door, and a coupling means,

Vwhich is movable transversely to the longitudinal direction of said rod-like member Vand connects said rod-like member .to said movable contacts, during the initial opening movements of said door, for displacing said movable contacts in responseto the initial opening movements of said door.

2. in a micro-wave oven: an oven space; a pivotal door through which access may be had to said oven space; a

' high frequency generator coupled to said oven space for l Y termined value and for releasing the engagement between said balls land said groove when said predetermined spacing has been reached, to thereby interrupt the connection between saidrnovable contacts and said door.

4. In a micro-wave oven: means enclosing an oven space; a pivotal door in said space-enclosing means through which door access maybe had to said oven space;

a high frequency generator coupled to said oven space for supplying high frequency energy thereto; circuit means connecting said high frequency generator with terminals to be conected to yan electric supply system; a Voltage converting and increasing means interconnected in said circuit means; a switch interconected iny saidV circuit means between said terminalsV and said voltage converting and increasing means and having at least one pair of stationary contacts and at least one pair of movable contacts, said movable contacts being conductivelyk interconnected and adapted to bridge said stationary contacts in they operative positionrof saidrmovable contacts; and a movement transmitting assembly positively connecting said door with the movable'contacts of Vsaid switch at least during the initial opening movement of said door and comprising a sleeve-like ball holder rigidly connected to said movable contacts, a rod-like member which is linked to said door the movements of said ball holder, said rod-.like member being adapted to be released by said balls at the end of the initial portion of the opening movement of said door and to be reconnected, during the corresponding portion of the closing movement of said door to said ballholder for causing said ball holder to close said switch.

tion of said movable contacts; and a movement transmity ting assembly comprising a first means, compulsorily movable together'with said movable contacts, a second means compulsorily movable together with said door, and a releasable coupling between said first and second movable means controlled in dependence of the movements of at least one of said first and second movable means, said second movable means being adapted to be released by the coupling at the end of the initial portion of the opening movement of said door and to be reconnected, during the corresponding portion of the closing movement of said door, to said first movable means for causing said first movable means to close said switch.

3. In a micro-wave oven: an oven space; a pivotal door through which access may be had to said oven space; a high frequency generator coupled to said oven space for supplying high frequency energy thereto; circuit means connecting said high frequency generator with terminals to be connected to an electric supply system; a voltage converting and increasing means interconnected in said circuit means; a switch interconnected in Said circuit means between said terminals and said voltage convertingV and increasing means and having at leastvone pair of stationary contacts and at least one pair of movable contacts, said movable contacts being conductively interconnected and adapted to bridge said stationary contacts in the operative position of said movable contacts; and a mechanical connection positively connecting said door with the movable contacts of said switch at least during the initial opening movement of said door and comprising a rod-like member which is linked to said door, is movable approximately Vin its longitudinal direction in response to the opening movements of said door andhas a circumferentially extending groove, a sleeve-like ball holder rig-y idly connected to said movable contacts and a plurality of balls held by said ball holder and cooperating with said groove, a stationary sleeve encircling said ball holder for maintaining said balls in engagement with said groove as long as said movable contacts bridge said stationary contacts and untilthe spacing between said movable contacts and said stationary contacts has reached a predev5. In a micro-wave oven: means enclosing an oven space; a pivotal door in said space-enclosing means through which door access may be had to said oven space; a high frequency generator coupled to said oven space for to'be connected to an electric supply system; a voltage con-V verting and increasing means interconnected in said cir cuit means,l a switch interconnected in said circuit means between said terminals and said voltage converting and increasing means and having at least one pair of stationary contacts and at least one pair of movable contacts, said movable contacts being conductively interconnected and adapted'to bridge said stationary contacts in the operative position of said movable contacts; and a mechanical con` nection positively connecting said door with the movable contacts of said switch at least during the initial opening movement of said door and comprising a rod-like member which is linked to said door, is movable approxi-V mately in itsrlongitudinal direction in response to the opening movements of said door and has a substantially V-shaped notch, a rod rigidly secured to said movable contacts, a leaf spring having a substantially V-sl1aped pori tion, and a substantially flat portion permanently engaging said rod, Said V-shaped portion being in engagement with said V-shaped notch when said movable contacts bridge said stationary contacts Vand in engagement with a longitudinal edge of said rod-like member when the spacing between said movable contacts and said stationary contacts has reached a predetermined minimum value.

References Citedby the Examiner UNITED STATES PATENTS Sawada Y. 219-l0.55

RICHARD M. WOOD, Primary Examiner. MAX L. LEVY, Examiner. 

1. IN A MICRO-WAVE OVEN: AN OVEN SPACE; A PIVOTAL DOOR THROUGH WHICH ACCESS MAY BE HAD TO SAID OVEN SPACE; A HIGH FREQUENCY GENERATOR COUPLED TO SAID OVER SPACE FOR SUPPLYING HIGH FREQUENCY ENERGY THERETO; CIRCUIT MEANS CONNECTING SAID HIGH FREQUENCY GENERATOR WITH TERMINALS TO BE CONNECTED TO AN ELECTRIC SUPPLY SYSTEM; A VOLTAGE CONVERTING AND INCREASING MENS INTERCONNECTED IN SAID CIRCUIT MEANS; A SWITCH INTERCONNECTED IN SAID CIRCUIT MEANS BETWEEN SAID TERMINALS AND SAID VOLTAGE CONVERTING AND INCREASING MEANS AND HAVING AT LEAST ONE PAIR OF STATIONARY CONTACTS AND AT LEAST ONE PAIR OF MOVABLE CONTACTS, SAID MOVABLE CONTACTS BEING CONDUCTIVELY INTERCONNECTED AND ADAPTED TO BRIDGE SAID STATIONARY CONTACTS IN THE OPERATIVE POSITION OF SAID MOVABLE CONTACTS, AND A MECHANICAL CONNECTION, POSITIVELY CONNECTING SAID DOOR WITH THE MOVABLE CONTACTS OF SAID SWITCH DURING THE INITIAL OPENING MOVEMENT OF SAID DOOR AND COMPRISING A ROD-LIKE MEMBER, SAID ROD-LIKE MEMBER BEING LINKED TO SAID DOOR ADJACENT TO THE PIVOT AXIS OF SAID DOOR AND MOVABLE APPROXIMATELY IN ITS LONGITUDINAL DIRECTION IN RESPONSE TO OPENING MOVEMENTS OF SAID DOOR, AND A COUPLING MEANS, WHICH IS MOVABLE TRANSVERSLY TO THE LONGITUDINAL DIRECTION OF SAID ROD-LIKE MEMBER AND CONNECTS SAID ROD-LIKE MEMBER TO SAID MOVABLE CONTACTS, DURING THE INITIAL OPENING MOVEMENT OF SAID DOOR, FOR DISPLACING SAID MOVABLE CONTACTS IN RESPONSE TO THE INITIAL OPENING MOVEMENTS OF SAID DOOR. 